81 Blackface with Blue Back Speakers Restoration Project/ Need Advice!
A while ago I picked up this amp in the used section of a national music store.
The Good News:
It had really nice tone, so much better than the newer reissues that were in the store. I tried all the new stuff, but nothing sounded as good.... Got it for $350 which seemed a good buy.
The Bad News:
A strong ground buzz sound that stayed constant regardless of volume changes.
It died after a month, took it to a tech guy, he got it working again, said it was a diode gone bad.
A few months later it died again. Used a different tech and he said a diode went bad and it had a bad output tube.
It' just died again for a third time. Ground Buzz but no sound from the guitar input.
This time I thought I should take a look at the inside. I am not a tech, but have an interest in learning. I know to only use one hand with the other in the pocket when probing voltages with ground clipped to chassis and not in my other hand. I check the voltages at the main caps to make sure they are back to safe levels. Takes about 3 or 4 minutes to drain. I always check regardless.
I have a tube tester, they all test good now. I have a Fluke meter and have checked voltages on the output pins and they all look good, both the positive and negative DC currents.
I tested the capacitors under the top cover and replaced two of them that were a bit out of spec on the micro ferret meter. Turned it over and replaced a couple more caps that were a bit off on the meter.
The main power transformer is providing 165 volts from the red wire to their initial contacts.
The output transformer is showing continuity from the blue and blue striped wires. It was showing 450 volts at one of the contact points... don't remember the color of that wire, but could re check.
What I did notice was someone in the past did some kind of modification at the 3rd farthest tube from the main output tubes. A capacitor (silver tube) from the board I could see was cut out and removed along with what I think are two resistors. This AX7 tube certainly runs hotter than the other ones. There looks like some kind of jump around the tube socket and an additional ground was soldered to the chassis with two resistors between the tube socket and ground.
I would like to put this back to original spec as I suspect this might be part of the problem.. don't know if this is a common mod or not... That amp has played with that mod ... so don't know.
So it's now a buzz, and no sound to the speaker other than the buzz..
any ideas or places I should look? I hate the idea of taking it to another unconfirmed tech. I'm in the SF Bay area.
Re: 81 Blackface with Blue Back Speakers Restoration Project/ Need Advice!
Welcome to the forum.
Pictures please.
Re: 81 Blackface with Blue Back Speakers Restoration Project/ Need Advice!
Re: 81 Blackface with Blue Back Speakers Restoration Project/ Need Advice!
Sorry, this is tube #3... or the 3rd small tube to the right of the main output tubes.
http://tributarymusic.com/fender_twin/solder.jpg
Re: 81 Blackface with Blue Back Speakers Restoration Project/ Need Advice!
Re: 81 Blackface with Blue Back Speakers Restoration Project/ Need Advice!
I tried to match up 3 photos to get the whole view....
http://tributarymusic.com/fender_twin/overview.jpg
